Hardy-Weinberg Principle

Hardy-Weinberg Principle

• Describes a population with constant allele frequencies across generations, assuming specific conditions are met.
• Equation: p²+2pq+q²=1
  • p² = frequency of homozygous dominant genotype (R₁R₁)
  • 2pq = frequency of heterozygous genotype (R₁R₂)
  • q² = frequency of homozygous recessive genotype (R₂R₂)

Hardy-Weinberg Equilibrium Conditions

• No mutations can be introduced to the gene pool
• Random mating has to occur with no preference based on the genotype
• No natural selection, meaning all individuals have equal reproductive success
• Large population size needed to prevent genetic drift altering allele frequencies
• No gene flow, meaning no migration of individuals in or out of the population

Application of the Hardy-Weinberg Principle

• Considering a plant species with two flower color alleles allows demonstration of the principle:
  • R₁ (Red Flowers): Frequency p = 0.7
  • R₂ (White Flowers): Frequency q = 0.3
• R₁R₁ (Red Flowers) → p^2 = (0.7) = 0.49 (49%)
• R₁R₂ (Pink Flowers) → 2pq = 2(0.7)(0.3) = 0.42(42%)
• R₂R₂ (White Flowers) → q^2 = (0.3)^2 = 0.09 (9%)
• Population is in Hardy-Weinberg equilibrium if these proportions remain unchanged across generations

Importance of the Hardy-Weinberg Principle

• Serves as a baseline for detecting evolutionary changes
• Deviation from expected frequencies suggests evolutionary forces, such as natural selection, genetic drift, and mutations, are at play
• Aids scientists in studying genetic disorders, population genetics, and evolutionary biology
• Predicts genetic stability or changes in populations, giving insight to evolutionary forces.

Genetic Mechanisms Altering Gene and Genotype Frequencies

• Mutation: Changes in DNA sequence introducing new alleles, which can be beneficial, neutral, or harmful, contributing to genetic diversity and evolution
• Selection: Natural selection favors individuals with beneficial traits, increasing reproductive success; positive selection increases beneficial traits, negative selection decreases harmful ones
• Gene Flow (Migration): Movement of individuals and genes between populations, introducing new alleles and potentially disrupting genetic equilibrium
• Genetic Drift: Random allele frequency fluctuations, more significant in small populations, potentially leading to loss or fixation of alleles

Demonstration of Selection's Effects on Gene Frequencies

• Observations in a population undergoing selection against the white fish phenotype show:
  • Frequency of ‘p’ (black fish allele) increases
  • Frequency of ‘q’ (white fish allele) decreases
  • Homozygous recessive genotype (q^2) declines
  • Heterozygous genotype (2pq) initially remains stable, then declines
  • Homozygous dominant genotype (p^2) steadily increases

Graphical Representation of Frequency Changes

• Graph 1: Gene Frequency Changes (p and q) Over Generations

  • X-axis: Generations (1 to 5)
  • Y-axis: Frequency of p and q
  • Shows p increasing and q decreasing

• Graph 2: Genotype Frequency Changes (p^2, 2pq, and q^2) Over Generations

  • X-axis: Generations (1 to 5)
  • Y-axis: Genotype frequency
  • Shows p^2 increasing, q^2 decreasing, and 2pq fluctuating

Calculation of Gene Frequency Change

• Demonstrates the calculation for change from Generation 1 to 2:
  • Δp = p2 – p1 = 0.37 – 0.34 = 0.03
  • Δq = q2 – q1 = 0.63 – 0.66 = -0.03

Key Points

• Selection against the white fish phenotype increases p and decreases q
• Hardy-Weinberg equilibrium gets disrupted when selection operates
• Populations evolve toward more black fish due to selective pressure
• These principles explain how populations genetically change and lead to evolutionary shifts

Teacher Tips

• Ensure students understand each mechanism’s effects on allele frequencies
• Tools for doing this
• Use locally available fish-shaped crackers for a hands-on activity
• Pause to ensure calculations are actively processed
• Encourage discussions on how genetic changes lead to species evolution

Species definition

• Biological definition
  • Species interbreed within the natural populations
  • Have reproductive isolation with other groups
• Ernst Mayr’s Definition
  • Consistent with the biological definition of species

Reproductive Isolation

• Definition
  • Prevents gene flow, leading to speciation.
• Two main types:
  • Pre-zygotic Isolation Mechanisms
  • Post-zygotic Isolation Mechanisms

Pre-zygotic Isolation

• Definition
  • Prevents fertilization and zygote formation
  • Types
  • Geographic/Ecological/Habitat Isolation
    • Species do not come into contact since environments are different
  • Temporal/Seasonal Isolation
    • Species reproduce at different times (seasonal, monthly, or yearly)
  • Behavioral Isolation
    • Species have different courtship behaviors
  • Mechanical Isolation
    • Differences in reproductive organs cause prevention of interbreeding
  • Gametic Isolation
    • Sperm and egg are incompatible, preventing fertilization

Post-zygotic Isolation

• Definition
  • Allows fertilization but the result is either nonviable or weak/sterile hybrids
  • Types
  • Hybrid Inviability
    • Fertilized eggs do not develop past early embryonic stages
  • Hybrid Sterility
    • Hybrids are sterile due to abnormal gonad development or chromosome segregation during meiosis
  • Hybrid Breakdown
    • F1 hybrids are viable and fertile
    • F2 hybrids display reduced viability or sterility

Genetic Mechanisms and Speciation

• Definition
  • Gene frequencies change with mutation, genetic drift, natural selection, and gene flow.
• Reproductive Isolation
  • Genetic divergence occurs, and eventually there will be speciation.

Modes of Speciation

Allopatric Speciation (Geographic Speciation)

• Allo = other
• Patric = place (‘other place’)
• Definition
  • Occurs when gene flow gets prevented when populations are geographically separated
• Example
  • Mountain ranges and bodies of water acting as barriers.

Sympatric Speciation

• Sym = same

• Patric = place (‘same place’)

• Definition

  • A population diverges into different species due to genetic changes within the same area

• Example

  • Polyploidization in plants since the chromosome number changes.

Parapatric Speciation

• Para = beside
• Patric = place (‘beside each other’)
• Definition
  • Distinct species evolve when populations border geographically
• Requires strong disruptive selection alongside environmental differences across borders.

Diagram of Speciation Models

• Illustrates the differences between Allopatric, Sympatric, and Parapatric Speciation by using diagrams
• Explains how species formation occurs with these models over time.

Evolution and Speciation Evidence

• Definition
  • Present-day species came from earlier species
  • Supported by
  • Morphological and anatomical data
  • Homology: shared structures due to a common ancestor
  • Molecular data: DNA and protein sequences
  • Biogeography: species distribution through time and space
  • Embryology: similarities in early development

Carolus Linnaeus

• Created a system for classifying organisms using the Binomial nomenclature
• Founded a hierarchical classification system and grouped via shared characteristics
• Provided a foundation for later evolutionary theories due to recognizing order in diversification of life

Thomas Malthus

• Wrote ‘Essay on the Principle of Population’.
• Proposed that populations would grow exponentially, while resources grow arithmetically, thus competition for survival
• His work influenced Darwin’s concept of struggle for existence

Georges Cuvier

• Founded paleontology: the study of fossils
• Developed the theory of Catastrophism, as natural disasters would cause species extinctions, then there would be new creations

James Hutton

• Gradualism theory: The idea that long periods of changes add up
• Stated that earth's features were caused by continuous and slow processes

Charles Lyell

• Wrote Principles of Geology
• He states that geological processes always operated the same
• This contributed to Darwin's work which suggested that the Earth was much older

Jean-Baptiste Lamarck

• Use and Disuse
  • The theory that through need, an organism will evolve or devolve
• Example: Giraffes eat from tall trees so their necks lengthen
• Inheritance of Acquired Characteristics
  • Offspring gain traits that their parents gained in a lifetime
  • Was later proven false

Charles Darwin

• HMS Beagle provided key insights into species variation
  • Observed finches that had different beak shapes based on thier diet
  • Studied giant tortoises and iguanas and thier environmental adaptations
• Questioned the idea of species fixity
• He began to notice similarities and differences of species based on location, allowing Darwin to suggest comman ancestry
• Selective breeding to understand natural selection
• Applied Malthus's ideas to explain competition

Charles Darwin Writing

• Species are created through the process of natural selection
• Inspired and worked with Alfred Wallace Russel
• 1859 published On the Origin of Species

Charles Darwin's Theory of Evolution

• Descent with modification -Species will evolve
• Inherited differences exist
• Artificial selection
• Humans breeding organisms for traits
• Nature selects
  • Adaptation: Traits that benefit the species

Neo-Darwinism

• Unified theory of evolution connecting Darwins and genetics
• Mendel provided explanations for heritability
• Theodosius Dobzhansky, Ronald Fisher, and Sewall Wright all contributed to the integration of genetics

Evidence for Common Ancestry

• Biogeography supports evolution via distribution
• Comparative Embryology; Similarities between embryonic stages can be signs of similar ancestors
• Fossils and transitional fossils

###Fossils

• Are preserved remains that show speciation -Examples are Archaeopteryx/Tiktaalik
• Allows scientists to compare data and development over time

Comparative Anatomy

• Homologous Structures are parts found across species that suggest a shared origin, even if those parts serve a new purpose
• Analogous Structures are features that function the same due to convergent evolution
• Vestigial Structures are parts that once had a purpose of function

Embryology

• There are characteristics during the development stage that suggest evolution
• Embryonic forms can become vestigial parts

Evidence From Molecular Biology

• Common ancestry can be proven, and tested with DNA/RNA
• Molecular Clocks prove a common origin in the biochemical
• Mutation studies

Molecular Evidence

• Biomolecules, like proteins and DNA, prove an evolutionary relationship
• Scientist compare Amino acids from cytochromes
• The relationships can be made visual be designing evolutionary trees/cladograms

Biogeography

• Species share trait based on location. Island species are unique due to thier isolation.

Recent Evolutionary Evidence

• Antibiotic resistance to bacteria is another proof
  • Examples are Finches evolving to produce different beaks due to environmental shifts

Taxonomy Overview

• Is structured, allowing easy understanding of evolutionary life -It can be defined as Hierarchy, Classification, Nomenclature, Identification, Description

Key Concepts for Systematics

• Carl Linnaeus created the binomial nomenclature
• There is Phylogenetic and Linnaean classification
• The tool commonly is Dichotomous key

Hierarchy

• Can be visualized from the Pyramid
• Kingdom at the top
• Then it goes -Phylum
• Class -Order -Family -Genus -Species at the bottom

Dichotomous Terms

• Are as follows
• Basal, Axillary, Folliage, Fascicled, Berry, Globose, Petiole, Raceme, Solitary, Terminal, Scutes, Posterior and Imbricate

Essential Information; Systematics

• Binomial nomenclature Hierarchical structure, Dichotomous keys are common tools in life
• "Taxonomy is very effective tool to learn throughout your studies

Cladistics Information

• Is defined with "Shared derived characters
• Group share traits from one ancestors.
• Done with Cladograms

Memorize Terms

• Phylogeny is evolutionary relationships

• Cladogram indicates derived traits are related

• Characters: What make up a organism

• Character state is form of character

• Taxa are shared ancestry

• Analogous is similar traits but different structure and origin

Reproduction Mode Types

• asexual is making copies of itself

  • ex -Fission for Paramecium
  • fragmentation Sporulation

• Isogamy has same gametes

• Heterogamy- animal and plant

Assexual VS. Sexual

• Asexual -Clones
• Rapid with less energy use
• Sexual -Genetically different offspring that spend more energy

Life cycles

• Cycles repeat

• Development stages are important

• Definitions that Need to Be Understood are all Vocabulary terms

• Cycle Phases; Menstrual

• What Hormones change

• Contraception

• Terms to memorize-

• -Abortion

• -Gametogenis ""Meiosis: "" is needed